Note 18 — Chapter XIII · POTASSIUM, RUBIDIUM, CÆSIUM, AND LITHIUM. SPECTRUM ANALYSIS

A. Scott (1887) determined the vapour densities of many of the alkali elements and their compounds in a platinum vessel heated in a furnace and previously filled with nitrogen. But these, the first data concerning a subject of great importance, have not yet been sufficiently fully described, nor have they received as much attention as could be desired. Taking the density of hydrogen as unity, Scott found the vapour densities of the following substances to be—

Na 12·75 (11·5). KI 92 (84).

K 19 (19·5). RbCl 70 (60).

CsCl 89·5 (84·2). CsI 133 (130).

FeCl₃ 68. AgCl 80 (71·7).

In brackets are given the densities corresponding with the formulæ, according to Avogadro-Gerhardt's law. This figure is not given for FeCl₃, because in all probability under these conditions (the temperature at which it was determined) a portion of the FeCl₃ was decomposed. If it was not decomposed, then a density 81 would correspond with the formula FeCl₃, and if the decomposition were Fe₂Cl₆ = 2FeCl₂ + Cl₂, then the density should be 54. With regard to the silver chloride, there is reason to think that the platinum decomposed this salt. The majority of Scott's results so closely correspond with the formulæ that a better concord cannot be expected in such determinations. V. Meyer (1887) gives 93 as the density of KI.